Characterization of reference sources for in situ calibration of activimeters with validation using Monte Carlo simulation

According to the CNEN-NN-3.05 (2013), a Nuclear Medicine Service (NMS) must contain at least one activimeter in operation, which is used on a mandatory and daily basis. Thus, in order to ensure that the routine of procedures in a NMS is not interrupted and to avoid probable damage on equipment to be moved, it's easy to justify favoritism through the implementation 'in situ' calibration technique. In this work, four radionuclides were characterized: ⁶⁷Ga, ²⁰¹Tl, ¹³¹I and ^99mTc, they were experimentally measured using an activimeter. The answers obtained were compared using the penEasy program, as general based on the PENELOPE Monte Carlo system, to study the response in the CRC-25R ionization chamber varying parameters that influence its response characteristics. The radionuclides under study showed similar behavior between them through simulation and a standard behavior in the experimental results. The height of the most efficient activimeter depends on the radionuclide and the volume inside the vial. Therefore, the height with greater efficiency depends on the radionuclide and the volume inside the vial. However, it's necessary to establish correction factors for each sample, geometry and volume considering the associated uncertainties. It's possible to observe a relationship between the vial and the distance from the bottom of the detector, which assumes an increasing behavior. The greatest deposition of energy can be measured between 5cm and 7cm in relation to the bottom of the well. From these heights, photons start to escape from the detector through the opening of the equipment, reducing the efficiency of the sensitive volume in absorbing the photons by approximately ±20%. (author)